236 COSMOS. 



rich to the Goldberg near Ormond, directed from south- 

 east to north-west ; on the other hand the Maars, from the 

 Meerfelder Maar to Mosbruch and the Laacher lake, follow 

 a line of direction from south-west to north-east. These 

 two primary directions intersect each other in the three 

 Maars of Daun. In the neighbourhood of the Laacher lake 

 trachyte is nowhere visible on the surface. The occurrence 

 of this rock below the surface is only indicated by the pecu- 

 liar nature of the perfectly felspar-like pumice-stone of 

 Laach, and by the bombs of augite and felspar thrown out. 

 But the trachytes of the Eifel, composed of felspar and 

 large crystals of hornblende, are only visibly distributed 

 amongst basaltic mountains : as in the Sellberg (1893 feet) 

 near Quiddelbach, in the rising ground of Struth, near 

 Kelberg, and in the wall-like mountain chain of Reimerath 

 near Boos." 



Next to the Lipari and Ponza Islands few parts of Europe 

 have probably produced a greater mass of pumice-stone 

 than this region of Germany, which, with a comparatively 

 small elevation, presents such various forms of volcanic 

 activity in its Maars (crate res d' explosion) , basaltic rocks, 

 and lava-emitting volcanoes. The principal mass of the 

 pumice-stone is situated between Nieder Mendig and Sorge, 

 Andernach and Hiibenach ; the principal mass of the duckstein, 

 or Trass (a very recent conglomerate, deposited by water), 

 lies in the valley of Brohl, from its opening into the Rhine 

 upwards to Burgbrohl, near Plaidt and Kruft. The Trass- 

 formation of the Brohl- valley contains, together with frag- 

 ments of grauwacke-slate and pieces of wood, small fragments 

 of pumice-stone, differing in nothing from the pumice-stone 

 which constitutes the superficial covering of the region, and 

 even that of the duckstein itself. Notwithstanding some 

 analogies which the Cordilleras appear to present, I have 

 always doubted whether the Trass can be ascribed to erup- 

 tions of mud from the lava-producing volcanoes of the Eifel. 

 I rather suppose, with H. von Dechen, that the pumice- 

 stone was thrown out dry, and that the Trass was formed in 

 the same way as other conglomerates. "Pumice-stone is 

 foreign to the Siebengebirge; and the great pumice-eruption 

 of the Eifel, the principal mass of which- still lies above the 

 loess (Trass) and alternates therewith in particular parts, 



